Postspaceflight orthostatic hypotension occurs mostly in women and is predicted by low vascular resistance

• Published in: Journal of applied physiology (1985) Vol. 92; no. 2; pp. 586 - 594
• Main Authors: Waters, Wendy W, Ziegler, Michael G, Meck, Janice V
• Format: Journal Article
• Language: English
• Published: Johnson Space Center Am Physiological Soc 01.02.2002; American Physiological Society
• Subjects: Adult; Aerospace Medicine; Anatomy & physiology; Applied physiology; Astronauts; Biological and medical sciences; Blood pressure; Blood Volume; Disease Susceptibility; Female; Forecasting; Hemodynamics; Human physiology applied to population studies and life conditions. Human ecophysiology; Humans; Hypotension, Orthostatic - etiology; Incidence; Male; Medical sciences; Plasma; Sex Characteristics; Space Flight; Space life sciences; Syncope - epidemiology; Syncope - etiology; Time Factors; Transports. Aerospace. Diving. Altitude; Vascular Resistance; Women; Nasa Discipline Cardiopulmonary; Manned; Short Duration; Flight Experiment; Nasa Center Jsc; Sts Shuttle Project; Human; Crew; Nervous system diseases; Cardiovascular control; Astronaut; Consciousness impairment; Space medicine; Sex; Plasma volume; Cardiovascular disease; Environmental factor; Weightlessness; Space flight; Postural hypotension; Vascular resistance; Syncope; Diseases of the autonomic nervous system; Risk factor; Neurological disorder; Microgravity; Space flight disease; NASA Discipline Cardiopulmonary; NASA Center JSC
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00544.2001

1  National Space Biomedical Research Institute, Baylor College of Medicine, Houston, Texas 77030; 2  Department of Medicine, University of California, San Diego, California 92103; and 3  Space Life Sciences Research Laboratories, National Aeronautics and Space Administration Johnson Space Center, Houston, Texas 77058 About 20% of astronauts suffer postspaceflight presyncope. We studied pre- to postflight (5- to 16-day missions) cardiovascular responses to standing in 35 astronauts to determine differences between 1 ) men and women and 2 ) presyncopal and nonpresyncopal groups. The groups were presyncopal women, presyncopal men, and nonpresyncopal men based on their ability to stand for 10 min postflight. Preflight, women and presyncopal men had low vascular resistance, with the women having the lowest. Postflight, women experienced higher rates of presyncope (100 vs. 20%; P  = 0.001) and greater losses of plasma volume (20 vs. 7%; P  < 0.05) than men. Also, presyncopal subjects had lower standing mean arterial pressure (P   0.001) and vascular resistance ( P  < 0.05), smaller increases in norepinephrine ( P    0.058) and greater increases in epinephrine ( P  0.058) than nonpresyncopal subjects. Presyncopal subjects had a strong dependence on plasma volume to maintain standing stroke volume. These findings suggest that postflight presyncope is greatest in women, and this can be ascribed to a combination of inherently low-resistance responses, a strong dependence on volume status, and relative hypoadrenergic responses. Conversely, high vascular resistance and postflight hyperadrenergic responses prevent presyncope. microgravity; gender; sympathetic; plasma volume; vascular resistance